This proposal describes a cooperative multidisciplinary prospective study of airborne acidic air pollutants and respiratory health of preadolescent children living in 36 communities in the eastern United States and Canada. In each community, the investigation will consist of one year of environmental monitoring followed by the administration of respiratory questionnaires and pulmonary function examinations to approximately 600 children. The environmental monitoring program will produce measures of average hydrogen ion concentrations during the one-year period and summer season preceding the health examinations, as well as comparable measures of size fractionated particulate concentrations (for two particle size cutoff values), sulfur dioxide, nitrogen dioxide, and ozone. These measures will continue during the time of the health assessment in each community. The health examinations will yield frequencies of respiratory illnesses and symptoms, along with measures of pulmonary function including FEV1, FEV75, FVC, MMEF, as well as measures of flow at low lung volumes. In addition, partial flow volume as well as full flow volume curves will be recorded. The primary hypotheses to be tested are that total acidity and fine particulate concentrations, are associated with measures of respiratory health. The sampling plan, involving both a large number of children and a large number of communities, will allow control for both between-child and geographic variability of the health outcomes. The monitoring methodology will provide separate measures of the contribution of sulfate and nitrate species to the total hydrogen ion concentration.